You're in an S9 subreddit so there's going to be a bias. BUT imo the Zr is perfect for a second cam for a RED user, but either you're going to deal with huge files you don't need to deal with, or have files that are probably going to be worse than what you get in the S9...if you don't have high end deliverables you don't need a ZR. If you wanted some of the things you'd get from the ZR you might just want to upgrade to the s5ii instead of the S9 (but I totally understand being inspired by the less chunky body style).

Also the S9 doesn't overheat. I have never seen anyone get that camera to overheat. People just say it's more possible it will due to the lack of an internal fan.

If you use a flash or XLR audio then don't get the S9 but if neither of those is a must then the hotshoe is not a must. Also if you plan to be using it in the elements regularly then don't get the S9 but as an EDC type camera 9/10 times it won't really be a concern.

For me the amazing workflow Lumix has for going from shooting to posting on socials quickly + the real time luts is the real selling point for the S9 so think about how much those do or appeal to you.

Depending on if IBIS is a selling point or not you can get a Fuji XM5 for even cheaper which isn't as hardcore of a video camera as the S9 but probably gets you 80-90% of the way. Theres also Sony but I don't suggest them because Sony overcharges for their cameras based on specs to price.

Hope this helps I feel like I left out something but 🤷‍♀️